The present invention concerns a method and device for driving a weaving machine in slow motion, i.e., at a lower than normal speed.
It is known that it must be possible for a weaving machine to be driven, apart from the normal speed, at a lower speed, both forward and backward, so as to make it possible for a number of weaving machine parts, such as the sley and the harnesses, to be positioned precisely.
Due to increasing weaving machine automation, for example the development of weaving machines having automatic weft repair functions, the accuracy with which the above-mentioned parts must be positioned has to meet ever more stringent demands.
Moreover, it is desirable that the time required to complete a certain action, such as the automatic repair of a weft thread, in which the sley must be successively put in different positions, be kept to a minimum.
It is generally known that for the slow motion of a weaving machine, or at least for the slow motion of a number of parts of the weaving machine, use is made of an auxiliary drive motor. In order to switch on the auxiliary drive motor during the slow motion, use is made of a slow motion clutch, for example as described in U.S. Pat. No. 4,592,392. This clutch provides for a large transmission ratio, such that the auxiliary drive motor can run at a normal speed, whereas the driven parts make a relatively slow movement.
The use of an auxiliary drive motor and slow motion clutch is disadvantageous in that the slow motion always has the same speed, depending on the transmission ratio and/or auxiliary drive motor used. In the case where a relatively low speed is used, there is a disadvantage in that the slow moving of the sley and/or the harnesses takes too much time. In the case where a relatively high speed is used, however, there is a disadvantage in that an exact positioning of the driven weaving machine parts is practically impossible, since it is very difficult then to bring these parts to a standstill in the required position.
It is also known to realize the slow motion drive by means of the main drive motor, by making this main drive motor run at a certain lower speed. To this end, the main drive motor can for example be excited via a separate, low frequency supply system. However, this known technique is disadvantageous in that the machine makes a very irregular movement and in that it is difficult to stop the machine at the required place.